Even small degrees of smoking have been shown to increase the risk for lung disease, according to a study published in the American Journal of Respiratory and Critical Care Medicine. Smoking affects lung disease in proportion to dose, providing further evidence that not smoking at all is superior to even low rates of smoking.

This prospective cohort study included 5115 young adults and was initiated in 1985. Follow-up examinations had the following retention rates: 2 years (91%), 5 years (86%), 7 years (81%), 10 years (79%), 15 years (74%), 20 years (72%), 25 years (72%), and 30 years (71%). Lung function decreased with smoking exposure, with the largest decrease in forced expiratory volume in 1 second (FEV1) in heavy stable smokers (–42.2 mL/y).

The risk for obstructive lung disease was nearly 8 times greater in heavy stable smokers compared with never-smokers, while the risk for emphysema was more than 20 times greater for heavy stable smokers. Quitters demonstrated a lower risk for emphysema than low-rate smokers as well as for rates of FEV1 decline (–33.8 mL/y and –35.7mL/y, respectively). The lower emphysema risk was despite greater number of mean lifetime pack-years (9.8 and 6.4, respectively, with 20 cigarettes per pack).

Participants’ smoking status was recorded during visits and phone interviews, with distinct patterns identified using zero-inflated Poisson trajectory modeling. This was done by including all participants who had ever smoked with data on how many cigarettes had been smoked per day for ≥3 of the 26 annual reports. FEV1 of <70% at year 30 was considered a threshold for incident obstructive lung physiology. Emphysema was identified using computed tomography scans. To investigate each smoking trajectory group’s association with emphysema at year 25 and obstructive lung physiology at year 30, logistic regression models were used.

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The researchers concluded that “[s]moking influenced lung disease risk in a dose-dependent manner. There was no safe threshold for smoking intensity on lung disease risk and even low-rate smokers were at increased risk for future lung disease. These results underscore the benefit of complete abstinence from smoking even among low rate smokers on respiratory outcomes.”

Reference

Mathew AR, Bhatt SP, Colangelo LA, et al. Life-course smoking trajectories and risk of emphysema in middle age: the CARDIA lung study [published online September 14, 2018]. Am J Respir Crit Care Med. doi:10.1164/rccm.201808-1568LE